溶胶凝胶合成MgB2超导纳米线介绍.ppt

* * A Simple Sol–Gel Synthesis of Superconducting MgB2 Nanowires Authors: Manashi Nath, B. A. Parkinson From: Advanced. Materials. 2006, 18, 1865–1868 第九组： 翟惠娟 (S 李月 (S 王若溪 (S 孙利 (S 鲁卉 (S 演讲人： 王若溪 (S 演讲日期：2007.12.31 Contents: 1. Introduction 2. Experimental and discussion 3. Conclusions 4. References 1. Introduction: · Superconductivity in MgB2 with a transition temperature (Tc) of near 39 K. · Higher Tc compared to other bimetallic compounds. 1.1 Advantages of MgB2: · Traditional solid-state synthesis routes. · Shapes are crystals, thin films, macroscopic wires, and tapes. 1.2 Look Back: Large differences in vapor pressure between Mg and B High reactivity of Mg towards O Carefully controlled conditions Doping or contamination of the MgB2 phase affects the superconducting Tc Most are multistep · Simple, high-yield, bulk synthesis · Pure MgB2 nanowires · Show a superconducting Tc of 38.6 K Make gel precursor 1.3 Sol-gel synthesis: Pyrolysis in B2H6-N2 atmosphere under ambient pressure 2. Experimental and discussion: MgBr2 + 2NaBH4 MgB2 + 2NaBr + 4H2 B2H6, N2 MgCl2, MgI2 Low yield Maintains a B-rich atmosphere If nominally pure N2 Black MgB2 phases and white MgO phases Impurity O2 Solid B-Oxide phases Even minute amounts of O2 2.1 Synthesis of Precursor Gel: NaBH4 0.078 g (ca. 2 mmol) Ethanol 6.8ml Sonication dissolve CTAB 0.025 mmol MgBr2·6H2O 0.2958 g (ca. 1 mmol) Sonication dissolve Ethanol 3.2ml CTAB 0.025 mmol Add dropwise to Gas, turbid Sonicate for several minutes Thicken over time and form a gel Open to the atmosphere for several hours 2.2 Synthesis of MgB2 Nanowires by Pyrolysis of the Gel: Quartz boat Horizontal tube furnace 800 ℃ Pyrolysis Black, powdery product 10 ℃/min B2H6, N2 5min Cool to r.t. 12 ~ 14 h Deionized water Wash rapidly Ethanol Wash rapidly NaBr, by-products Chemically pur